1. Field of the Invention
The present invention relates to a fastener means which utilizes the attraction of a permanent magnet and which comprises an attraction member and a member to be attracted. More particularly, in order to converge the magnetism of one of the magnetic poles, a projection made of ferromagnetic material is provided on a plate to be attached on the surface of the magnetic pole. The plate at the magnetic pole and the permanent magnet are firmly fixed by firmly pressing the projection into a hole provided in the direction of the magnetic pole of the permanent magnet to thereby form an attraction member. The member to be attracted is made of ferromagnetic material and is made attachable/detachable with respect to the surface of the other pole of the permanent magnet. By attaching the attraction member and the attracted member to the body and the flap of a handbag respectively, a fastener means is obtained. The fastener means may be attached to a body and a door of a case, or to both ends of a belt or a chain, or on a jacket at the position of a hook or a button, for opening and closing the door, fastening belts, connecting the chain, fastening cloths, etc.
2. Description of the Related Art
Fastener means utilizing the attraction of a permanent magnet are diversified in structure and use.
One of such fastener means is embodied by U.S. Pat. No. 4,021,891. The fastener means according to said invention features a ferromagnetic member which is attached fixedly or detachably to each respective magnetic pole of a magnet, thereby containing the magnetic fields of the poles within the respective plates. At the same time, a hole is provided in the direction of the magnetic pole so that a ferromagnetic projection arranged inside the hole forms a passage of low magnetism connecting the ferromagnetic plates.
As a result, the magnetic flux of the permanent magnet is converged on the ferromagnetic projection in the hole, minimizing the magnetic flux leakage and thus providing a fastener means with firm attraction.
Certain improvements have been made to U.S. Pat. No. 4,021,891 and these are shown in U.S. Design Pat. Nos. 247,467 and 247,468. U.S. Pat. No. 4,453,294 for a fastener means shows an additional improvement U.S. Pat. No. 4,489,361, discloses an additionally improved fastener means with higher shielding effect against magnetic leakage.
In the above mentioned patents, the ferromagnetic plate is attached to one of the magnetic poles either by a non-magnetic case, or by attaching the plate directly to the permanent magnet by an adhesive.
Use of a non-magnetic case as a means to attach the ferromagnetic member for the purpose of converging the magnetic flux is advantageous in that the non-magnetic case covers the outer surface of the magnet and, therefore, both protects the magnet against damage and offers a better appearance. However, the presence of the non-magnetic case causes a magnetic gap between the surface of the attraction member and the member to be attracted, equivalent to the thickness of the case. This prevents the magnetic flux of the attraction member from effectively reaching the member to be attached and causes flux leakage of the flux outside the fastener means.
Manufacturing difficulty is a second problem of the above mentioned means. The non-magnetic case is usually manufactured by press-holding. Thereafter, it is necessary to fix the permanent magnet and ferromagnetic plate within the case. This involves the handling of the several components, as well as troublesome assembling steps, and leads to a high cost for the final product.
In order to overcome both the magnetic gap and the production cost problems, one possible solution is to directly attach a ferromagnetic member to one of the magnetic poles of a permanent magnet with an adhesive. This eliminates the magnetic gap that is formed by a non-magnetic case, thereby improving the attraction between the magnet and the member to be attracted. However, in order to fabricate a fastener of this type, it is necessary to apply an adhesive, align the positions of a permanent magnet and the ferromagnetic plate, press the two members together in a manner that does not cause the adhesive to be squeezed out, and maintain the pressure between the two members until the adhesive is completely set. Once again, because of the numerous productions steps, the production cost becomes high. Furthermore, there is no ready method to check the condition of adhesion between the permanent magnet and the ferromagnetic plate, which results in a danger that the adhesion between the two members may be or may become ineffective and ultimately result in the parts separating from each other by subsequent impact.
Another fastener means, such as that disclosed in U.S. Pat. No. 4,700,436, includes a permanent magnet made of synthetic resin, utilizes a unique design wherein the ferromagnetic member is integrally buried inside the magnet. As a result, there is no need to attach the ferromagnetic member to one of the magnetic poles of the magnet. Nor is it necessary to attach the ferromagnetic member by means of a non-magnetic case. As a result, the problems encountered in the construction and/or manufacture of the prior art fastener means were solved.
However, the fastener means mentioned above has serious drawbacks. In particular, since the permanent magnet is made from synthetic resin by injection-molding extreme care must be exercised in incorporating the ferromagnetic member inside the resin. The procedure requires the use of a high degree of skill in carrying out a number of troublesome steps. Furthermore, the ferromagnetic member incorporated inside the magnet is likely to be at an undesired angle, making it difficult to establish firm attraction between the attraction member and the member to be attracted.